Laser with a monocrystalline ya10 {11 :n{11 {11 {11 {0 active medium

ABSTRACT

Nd 3 ions serve as a dopant in monocrystalline YA103 forming an active solid-state lasing medium.

United States Patent LASER WITH A MONOCRYSTALLINE YAlO3zNd ACTIVE MEDIUM 11 Claims, 1 Drawing Fig.

US. Cl 331/945, 252/301.3, 330/751 Int. Cl 1101s 3/16 Field of Search 331/945;

References Cited OTHER REFERENCES Ohlmon, Flourescence of Cr in LaA1O Bull. of the Am. Physics Soc. 1964, pp. 280- 1.

Ohlmon et al., Energy Transfer from 3d to 4f Electrons in 'LaAlO zcr, Nd Phys. Rev. Lett. 13 (4) 27 Jul. 64, pp. 135- Bums et al., Temperature Dependence of in Several Perovsketes, J. Applied Physics, vol. 37, Oct. 1966, pp.

Primary Examiner-William L. Sikes Assistant ExaminerR. J. Webster Attorneys-Harold A. Murphy and Joseph D. Pannone ABSTRACT: Nd ions serve as a dopant in monocrystalline YAlOg forming an active solid-state lasing medium.

PATENTEnum 19 law 4 62 llVVE/VTORS ROCH v. MOA/CHAMP MARVIN J. WEBER MICHAEL 5455 ATTORNEY g, LASER WITH A MONOCRYSTALLINE YAlOl'nNd ACTIVE MEDIUM SUMMARY OF THE INVENTION This invention relates to fluorescent materials and devices utilizing such materials. More particularly, the invention relates to laser materials and devices generating coherent light in the infrared region, especially in the wavelength range from 0.86 microns to 1.44 microns.

it is known that trivalent neodymium is an active laser ion producing coherent light in the infrared region when suitably stimulated. Nd ions have been used as a dopant in a calcium tungstate host lattice (U.S. Pat. No. 3,225,306 to L. F. Johnson) and glas (U.S. Pat. No. 3,270,290 to R. D. Maurer). These hosts sufler many disadvantages. For example, calcium tungstate is diflicult to fabricate due to its tendency to crack. Also, the tungtate crystal and glass have a low thermal conductivity which precludes their use with high average power pump sources.

Yttrium aluminum garnet (YAG), having the molecular formula Y,A1,o,,, is a monocrystalline laser host material found to be far more suitable for high-power pulse and CW laser operation. However, the power output of a suitably optically pumped YAG laser rod depends upon the concentration of Nd dopant, which in YAG is a maximum of 2X10 ions/cm, consistent with high optical quality required for lasing. Exceeding this maximum normally produces bubbles, second phase precipitants, and strain in YAG.

It is, accordingly, an object of this invention to devise a material capable of fluorescing in the infrared region, especially between 0.86 to 0.94, 1.05 to 1.11, and 1.31 to 1.44 microns. Relatedly, the material should be in the solid state and capable of high power pulse and CW operation. It should be resistant both to warping and cracking. Lastly, the material should exhibit rapid crystal growth, uniformity of doping, and ease of fabrication.

It is yet another object of this invention that the host materiall with its Nd dopant also permits the use of a codopant to enhance the efficiency with which the lasing medium may be optically pumped.

SUMMARY The above objects are satisfied in an embodiment in which an active laser medium is formed from monocrystalline YAlO host lattice, a portion of whose Y ions have been replaced by Nd ions with amounts of Cr added for the optically most efficient operation. With YAlO it is possible to replace a higher proportion of Y"* ions with Nd ions while still maintaining the high crystal quality suitable for laser use.

When the YAlO; crystals are grown according to the method found in copending US. Pat. application No. 886,932 to Roch R. Monchamp, Marvin J. Weber, and Edward M. Comperchio, entitled Single Crystal YAlO Laser Host Material and Method for Making Same, filed on Dec. 22, 1969, then the growth rates are substantially faster than those of YAG.

The drawing is a perspective view of an infrared device utilizing compositions of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Laser experiments were made using four laser rods formed from monocrystalline YAlO doped with respectively 1.3 X l", 6.9 X 10*, 3 X 10, and 1.6 X 10 Nd ions per cm". The rods were grown using the technique of the aforementioned copending application. These rods were typically 5 m.m. cross section diameter and length of 50 mm. As an example, the l.6 X ion/cc. doped rod was formed from a boule derived from a melt of 237.076 grams of Y,O 108.416 grams of A1 0 and 4.508 grams of Nd,o,. The melt was seeded with a YalO, crystal, which seed was rotated at 20 r.p.m. and pulled out of the melt at a rate of 0.300 inches per hour. The resulting crystal boule size was 75 millimeters in length with a cross section diameter varying between 10 to 11 millimeters. The crystal exhibited a violet color. The crystal orientation was approximately 7 from one of its optic axes.

The ends of each rod were finished flat and parallel with an antireflection coating of less than 0.25 percent reflectivity in the wavelength range between 0.86 to 1.44 microns. Mirrors were used and disposed opposite the finished flat rod ends and were also coated to have the proper reflectivity in this spectral region. The mirrors were used for both the pulsed and CW test operations.

CW laser studies were performed using two 2-inch arc length, 4 millimeter bore, krypton arc lamps in a gold plated double ellipse. The 1.6 X 10 Nd" ions/cc. doped rod produced 300 milliwatts of output at an input power of 4000 watts. Pulsed laser studies employed one 2-inch arc length, 4 millimeter bore, xenon flash lamp in a gold plated single ellipse.

The preferred lasing wavelength of these Nd doped rods was 1.0795 microns fl A. The emission was strongly linearly polarized in the plane of the optic axes. When a polarizer was placed within the laser davity and rotated so that there was no feedback for the preferred polarization, then lasing was obtained with the emission polarized in the orthogonal plane and with the wavelength being shifted to 1.0645 fl A. It was observed that the laser remained in the preferred polarization plane and wavelength until the polarizer was rotated more than 70 away from full transmission of the preferred polarization.

Referring now to the drawing, there is shown a rod shaped crystal 1 of YAlO having an appropriate concentration of Nd ions. Pump energy is supplied by a helical lamp 2 encompassing rod 1 and connected to an energy source not shown. Ends 3 and 4 of rod 1 are ground and polished in the form of confocal spherical surfaces. Reflective layers 5 and 6 are deposited on ends 3 and 4 thereby forming an optical cavity resonator.

Advantageously, layer 6 is totally reflecting while layer 5 includes at least a portion which is only partially reflecting to permit the escape of coherent radiation 7.

Lamp 2 is advantageously of a type which produces intense radiation of a broad band from 3,000 A to 9,000 A. Krypton or xenon lamps are considered useful to pump the material of the invention.

Although the invention has been described with reference to two specific embodiments, this is to be construed by way of illustration and does not limit the scope of the invention. For example, the material of the invention may be used with any concentration of neodymium or Nd and Cr ions compatible with good optical quality. Furthermore, the material may be used in optical cavity resonators other than the confocal type. The parallel plane resonator, as well as others, may also be employed. Other variations are also possible within the spirit of the invention.

We claim:

1. A laser comprising:

an optical cavity having an axis;

an active medium within the optical cavity placed along axis of said cavity comprising trivalent neodymium within the concentration range from 1 X 10 ions per cubic centimeter to 2 X 10" ions per cubic centimeter in a single crystal body of yttrium orthoaluminate; and

a source of illumination incident upon said active medium for pumping said active medium to establish a population inversion in said medium.

2. A laser having output radiation at a wavelength in the infrared region especially in the ranges from 0.86 to 0.94, 1.05 to 1.11, and 1.31 to 1.44 microns, comprising an active medimeans for pumping said medium to produce a population inversion therein;

said active medium being formed from a single crystal body of (A10 doped with Nd ions within the concentration range from 1 X 10 ions per cubic centimeter to 2 X 10" ions per cubic centimeter; and

means comprising an optical cavity having maximum reflectivity for the wavelengths in the aforementioned ranges and an axis, along which said active medium is placed for providing stimulated emission of radiation from said active medium via said cavity.

3. In a laser according to claim 2, wherein:

the active medium is in the form of a solid monocrystalline YAIO, rod whose end surfaces are optically permeable to the wavelength ranges of interest; and

the means comprising an optical cavity comprise a pair of mirrois, each minor being disposed opposite a corresponding rod end surface.

4. A laser comprising:

an active medium consisting essentially of monocrystalline YAIO, host lattice in which a portion of the Y ions have been replaced by Nd ions, the portion of the Y ions so replaced being less than 2 X ions per cubic centimeter;

means for producing population inversion between a pair of optically connected energy levels of said Nd ions; and means for stimulating coherent emission in the wavelength corresponding to the energy separation levels.

5. An active medium according to claim 4, in which the host lattice includes Cr codopant ions.

6. An active medium according to claim 4, wherein the active medium comprises a YAlO monocrystalline rod whose end faces are reflectively coated, thus forming an optical cavity.

7. A laser comprising:

an optical cavity having an axis a lasing medium within and along the axis of said optical cavity comprising trivalent neodymium in a single crystal yttrium orthoaluminate host; and

a source of illumination incident upon said lasing medium to produce a population inversion in said medium for pumping said lasing medium.

8. A laser amplifier comprising:

a single anisotropic orthorhombic crystal comprising yttrium orthoaluminate and trivalent ions of neodymium substituted at at least some of the lattice sites therein; and

means for pumping said crystal to produce a population inversion therein.

9. A laser comprising:

an active lasing medium comprising trivalent neodymium ions in a single crystal yttrium orthoaluminate host; and

means for pumping said active lasing medium to produce a population inversion therein.

10. A laser in accordance with claim 9 wherein said active lasing medium further includes trivalent chromium ions.

11. A laser having output radiation at a wavelength in the infrared region especially in the ranges from 0.86 to 0.94, 1.05 to 1.1 l, and 1.31 to 1.44 microns, which laser comprises:

an active medium comprising trivalent neodymium within the concentration range from 1 X 10 ions per cubic centimeter to 2 X 10 ions per cubic centimeter in a single crystal body of yttrium orthoaluminate;

means for pumping said active medium to produce a population inversion therein; and

means comprising an optical cavity having maximum reflectivity for the wavelengths in the aforementioned ranges and an axis, along which said active medium is placed for providing stimulated emission of radiation from said active medium via said cavity.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N 3,614.662 Dated October 19 1971 Inventor(8) Roch R. Moncham Ma It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the title, change "YAlO3:Nd to YAlO :Nd

Column 1, line 67, after "copending" insert U. S.

Column 2, Claim 1, line 56, after "along" insert the optical Column 3, Claim 7, line 30, after "axis" insert Column 4, Claim 7, lines 2 to 4, change "a source of illumination incident upon said lasing medium to produce a population inversion in said medium for pumping said lasing medium." to a source of illumination incident upon said lasing medium for pumping said lasing medium to produce a population in said medium.

Signed and sealed this 27th day of June 1 972.

(SEAL) Attest:

EDWARD M.F'LETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents USCOMM-DC scan-Pee 9 U,5 GDVERNMENY PRINTING OFFICE: l5. Cl-Il-SJ 

2. A laser having output radiation at a wavelength in the infrared region especially in the ranges from 0.86 to 0.94, 1.05 to 1.11, and 1.31 to 1.44 microns, comprising an active medium; means for pumping said medium to produce a population inversion therein; said active medium being formed from a single crystal body of YAlO3 doped with Nd 3 ions within the concentration range from 1 X 1019 ions per cubic centimeter to 2 X 1021 ions per cubic centimeter; and means comprising an optical cavity having maximum reflectivity for the wavelengths in the aforementioned ranges and an axis, along which said active medium is placed for providing stimulated emission of radiation from said active medium via said cavity.
 3. In a laser according to claim 2, wherein: the active medium is in the form of a solid monocrystalline YAlO3 rod whose end surfaces are optically permeable to the wavelength ranges of interest; and the means comprising an optical cavity comprise a pair of mirrors, each mirror being disposed opposite a corresponding rod end surface.
 4. A laser comprising: an active medium consisting essentially of monocrystalline YAlO3 host lattice in which a portion of the Y3 ions have been replaced by Nd 3 ions, the portion of the Y 3 ions so replaced being less than 2 X 1021 ions per cubic centimeter; means for producing population inversion between a pair of optically connected energy levels of said Nd 3 ions; and means for stimulating coherent emission in the wavelength corresponding to the energy separation levels.
 5. An active medium according to claim 4, in which the host lattice includes Cr 3 codopant ions.
 6. An active medium according to claim 4, wherein the active medium comprises a YAlO3 monocrystalline rod whose end faces are reflectively coated, thus forming an optical cavity.
 7. A laser comprising: an optical cavity having an axis a lasing medium within and along the axis of said optical cavity comprising trivalent neodymium in a single crystal yttrium orthoaluminate host; and a source of illumination incident upon said lasing medium to produce a population inversion in said medium for pumping said lasing medium.
 8. A laser amplifier comprising: a single anisotropic orthorhombic crystal comprising yttrium orthoaluminate and trivalent ions of neodymium substituted at at least some of the lattice sites therein; and means for pumping said crystal to produce a population inversion therein.
 9. A laser comprising: an active lasing medium comprising trivalent neodymium ions in a single crystal yttrium ortHoaluminate host; and means for pumping said active lasing medium to produce a population inversion therein.
 10. A laser in accordance with claim 9 wherein said active lasing medium further includes trivalent chromium ions.
 11. A laser having output radiation at a wavelength in the infrared region especially in the ranges from 0.86 to 0.94, 1.05 to 1.11, and 1.31 to 1.44 microns, which laser comprises: an active medium comprising trivalent neodymium within the concentration range from 1 X 1019 ions per cubic centimeter to 2 X 1021 ions per cubic centimeter in a single crystal body of yttrium orthoaluminate; means for pumping said active medium to produce a population inversion therein; and means comprising an optical cavity having maximum reflectivity for the wavelengths in the aforementioned ranges and an axis, along which said active medium is placed for providing stimulated emission of radiation from said active medium via said cavity. 